Gain-coupling type distributed feedback semiconductor laser and method for producing the same

Abstract

A gain-coupling type distributed feedback semiconductor laser device having a periodically varying gain along a cavity direction includes: a first periodic undulation formed along the cavity direction, the first periodic undulation including convex and concave portions; a semiconductor embedded layer formed on the first periodic undulation; and at least one active layer formed within the semiconductor embedded layer so as to extend along a direction which is perpendicular to the surface of a substrate, the at least one active layer being present on the concave portions of the first periodic undulation with a period which is substantially equal to a period of the first periodic undulation.

What is claimed is:  
     
       1. A gain-coupling type distributed feedback semiconductor laser device having a periodically varying gain along a cavity direction, comprising: 
       a first periodic undulation formed along the cavity direction, the first periodic undulation including convex and concave portions;  
       a semiconductor embedded layer formed on the first periodic undulation; and  
       at least one active layer formed within the semiconductor embedded layer so as to extend along a direction which is perpendicular to the surface of a substrate, the at least one active layer being present on the concave portions of the first periodic undulation with a period which is substantially equal to a period of the first periodic undulation.  
     
     
       2. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein the semiconductor embedded layer and the at least one active layer comprise a III-V group compound semiconductor containing at least one III group element and at least one V group element, the semiconductor embedded layer comprising the at least one III group element at a component ratio not equal to a component ratio at which the at least one active layer comprises the at least one III group element. 
     
     
       3. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein the at least one active layer comprises a vertical quantum well structure. 
     
     
       4. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein the at least one active layer is formed of a quantum well wire structure, at least one layer of the quantum well wire structure being provided along a direction which is perpendicular to the surface of the substrate. 
     
     
       5. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein at least two periodic undulations including the first periodic undulation are provided, the at least two periodic undulations comprise convex and concave portions which are formed in a same period and positions as that of the first periodic undulation. 
     
     
       6. A gain-coupling type distributed feedback semiconductor laser device according to claim  5 , wherein the at least two periodic undulations have substantially a same shape. 
     
     
       7. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein each of the concave portions of the periodic undulation comprises a flat portion having a width along the cavity direction which is in the range of about 0 nm to about 30 nm. 
     
     
       8. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein each of the concave portions of the periodic undulation comprises lateral surfaces formed of a (n 11 ) plane and a bottom formed of the ( 100 ) plane. 
     
     
       9. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein each of the concave portions has a depth equal to or greater than about 40 nm. 
     
     
       10. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein the semiconductor embedded layer comprises a III-V group compound semiconductor containing at least one III group element and at least one V group element, wherein the at least one III group element is selected from Al and Ga. 
     
     
       11. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein the semiconductor embedded layer comprises Al at a component ratio in the range of about 0.1 to about 0.3. 
     
     
       12. A gain-coupling type distributed feedback semiconductor laser device according to claim  5 , wherein at least one semiconductor layer is provided between the at least two periodic undulations, the semiconductor layer is formed of a compound semiconductor containing Al at a component ratio which is equal to or greater than about 0.45. 
     
     
       13. A gain-coupling type distributed feedback semiconductor laser device according to claim  1 , wherein the at least one active layer has a height which is equal to or greater than about 60 nm. 
     
     
       14. A method for producing a gain-coupling type distributed feedback semiconductor laser device having a periodically varying gain along a cavity direction, comprising the steps of: 
       forming a periodic undulation including convex and concave portions on a surface of a semiconductor; and  
       forming a semiconductor embedded layer formed on the periodic undulation, the semiconductor embedded layer including periodically disposed active layers.  
     
     
       15. A method for producing a gain-coupling type distributed feedback semiconductor laser device according to claim  14 , 
       wherein the semiconductor embedded layer comprises a III-V group compound semiconductor containing at least two III group elements having respective migration rates, and  
       wherein the step of forming the semiconductor embedded layer comprises forming the active layers so that the active layers comprise one of the at least two III group elements at a component ratio not equal to a component ratio at which the semiconductor embedded layer-comprises the one of the at least two III group elements.